1. Field of the Invention
The invention is related to the field of solid-state memories and, in particular, to a magnetic memory comprised of a three-dimensional stack of layers.
2. Statement of the Problem
Solid-state memory is a nonvolatile storage medium that uses no moving parts. Some examples of solid-state memory are flash memory and MRAM (magnetoresistive random access memory). Solid-state memories provide advantages over conventional disk drives in that data transfers to and from solid-state memories take place at a much higher speed than is possible with electromechanical disk drives. Solid-state memories may also have a longer operating life and may be more durable due to the lack of moving parts.
Solid-state memories are typically fabricated as a two-dimensional array of memory cells, also referred to as cross-point memory arrays. However, newer solid-state memories have been suggested that are three-dimensional. For example, U.S. Pat. No. 7,388,776 and U.S. Pat. No. 7,606,605 each describe a three-dimensional memory for storing data, and are incorporated by reference as if fully included herein. A three-dimensional memory includes a plurality of data storage layers that are stacked on top of one another. Each of these data storage layers is operable to store bits of data in the form of magnetic domains. If a page of bits is written into a first one of the data storage layers, the page of bits may be transferred up the stack to a secondary data storage layer. After the page of bits is transferred, a new page of bits may be written into the first data storage layer. This process may continue to store data up the stack of data storage layers. The three-dimensional memory allows for a large increase in storage capacity, and thus, the storage capacity of solid-state memories may approach the storage capacity of electromechanical disk drives.